The purpose of this study is to determine the incidence, risk factors, and viral etiology of malignancy in hemophiliacs infected with human immunodeficiency virus (HIV). Approximately 4000 hemophiliacs from 20 U.S. Hemophilia treatment centers (HTCs) will be available for study, representing one-fifth of the entire U.S. hemophilia population. This group is unique in that patients are well characterized and closely followed, the time of HIV infection is known, the probability is now low, and the incidence of AIDS and malignancy is increasing. The specific objectives include: 1. A prospective incidence study in which 4000 subjects (> 4 years) are enrolled, both HIV(+) and HIV(-), and followed for development of AIDS and malignancy. 2. A retrospective review of all past AIDS cases, malignancies, and deaths in HIV(+) hemophiliacs to determine incidence of AIDS and lymphomas in the ten geographic regions. Biopsy and autopsy slides from past cases will be reviewed to determine the incidence of malignancy. 3. A nested case-control study comparing incident lymphoma cases identified in the prospective study with four-matched HIV(+) controls, matched for age and duration of infection, to determine clinical, laboratory, and life-style characteristics associated with malignancy development. 4. A molecular biology study using EBV and HIV probes to study biopsy/autopsy material and sera from cancer cases. All prospectively identified autopsy cases will be performed according to a standardized protocol and all slides reviewed.